Generally, an electric tool comprises a motor that has an output appropriate for the intended use. Then, when the electric tool comprises a removable battery pack as a power supply, the battery pack has a voltage and a capacity corresponding to the output of the motor. For this reason, when there are several different types of electric tools, it means that there are also several different types of battery packs that have voltages and capacities corresponding to the several different types of electric tools, respectively.
In regard to these several different types of battery packs, Japanese Patent Application Laid-Open No. 2002-027675 discloses an electric tool which is configured to be able to use a battery pack under some conditions with relation to a voltage, even if the battery pack is not the proper corresponding battery pack.
In the above document, when a proper battery pack corresponding to an electric tool has a rated output voltage of “A” and other battery packs have a rated output voltage of “A” or less, these other battery packs can be also connected to the electric tool and can be also used.
Then, the electric tool can not use an upper battery pack that has a higher rated output voltage than the proper battery pack, and this is desirable from a safety standpoint. However, when the proper battery pack has been used up and there is only an upper battery pack around and a user wishes to work using the upper battery pack for only a short time, the electric tool can not meet the user's demand.
As a matter of course, if the electric tool is configured so as to be able to likewise use the upper battery pack, the electric tool can meet the user's demand. However, when the upper battery pack has been connected and used for a long time, the motor may break down easily due to the temperature rise, or the user may feel uncomfortable due to the temperature rise of the tool or may burn his hand with the tool.